Magnetic work holder



y 2 1949. s. 1. HITCHCOCK 2,471,067

MAGNETIC WORK HOLDER Filed Oct. 19, 1945 2 Sheets-Sheet l izyi. 2

My WQ/if W 10 14 L 51 r::: i.-. A -17 .1 4 13 25"" 13 11 u I n 5 l 11 IQ 10 "-0 PM :IU' 50 INVENTOR ATTORNEY May 24, 1949. 's. l. HITCHCOCKMAGNETIC WORK HOLDER 2 Sheets-Sheet 2 Filed Oct. .19, 1945 INVENTORYZ'ANLEY ISAZAHH TCHCOQK BY% .a M.

ATTORNEY Patented May 24, 1949 MAGNETIC WORK HOLDER Stanley IsaiahHitchco London, England, as-

signor to Tropical Plantations Limited, London,

England Application October 19, 1945, Serial No. 623,219 In GreatBritain November 6, 1944 7 Claims. 1

Although applicable to magnetic workholders generally utilisingpermanent magnets for the retention of the work in position, andconsequently including rotary magnetic chucks, the invention isparticularly concerned with a magnetic workholder of the kind which isintended to maintain a workpiece or series of workpieces in .astationary position during a grinding or other operation, the holderbeing intended either to be placed on a bench or other supportingsurface, in .a vice, or even held in the hand Whilst the machining orother operation is being performed on the workpiece or workpieces.

,It has previously been proposed in the construc: ticn of such magneticworkholders to arrange the permanent magnet or magnets so that it orthey are capable of controlled movement to cause the lines of magneticflux to be diverted from their normal course in which they pass throughthe workpiece, and thus retain the latter in position on the face of theholding device, into a position in which the lines of magnetic fluxwholly or mainly pass along .an alternative path which does not includethe workpiece, and consequently permit of the removal of the latter fromthe Workpiece-supporting face. It will be appreciated, therefore, thatthe magnet or magnets is or are capable of being moved into either oftwo alternative positions, thus rendering the workholding deviceoperative or inoperative at will.

In :such workholclers as previously proposed it has been the practice toarrange the pole faces of the permanent magnet or magnets in contactwith the workpiece-supporting face plate, or with armature membersassociated therewith, and consequently it was not only necessary togrind the rubbing faces of the magnets and their cooperating ,partsaccurately to ensure the parts being relatively movable, but the factthat the parts were actually in rubbing contact necessarily increasedthe effort required to produce relative rotational or slidin movementbetween the parts when it Was desired to bring the workholder into orout of operation.

The chief object of the present invention is to evolve a workholder of amore simple construction than hitherto, involving the minimum number ofcomponent parts; and which, furthermore, can be operated with theminimum of effort and in a simple manner.

The magnetic workholder according to the present invention comprises aworlosupporting surface incorporating soft iron or similar members, apermanent magnet mounted for angular movement about an axis situated atright-angles to its magnetic axis and capable of angular movement intoeither of two alternative positions in which the work will be heldmagnetically in position on the work-supporting surface and releasedtherefrom, and fixed armature members located on opposite sides of saidmagnet and in spaced relationship to the magnets pole faces, saidarmature members being in contact with or in close proximity to theworlbsupporting surface and when the magnet is in its operativeworkholding position servin to connect the north and south polemagnetically to the work-supporting surface and work so that the linesof magnetic force pass freely through the soft iron members of theworksupporting surface and work, and when the magnet is in itsalternative inoperative position together bridge north and south polesto provide alternative paths for the lines of magnetic flux of lowerreluctance so that all or the majority of the lines of magnetic fluxwill no longer pass through. the Work and workholding surface and thuspermit of the workpieces removal.

It will be appreciated therefore that, due to the fact that the polefaces of the permanent magnet do not actually contact the armaturemembers but merely lie in close pr Ximity thereto, the permanent magnetcapable of being moved angularly into either alternative position Withthe minimum of c-fiort on the part of the operator, the permanent magnetbeing preferably of partcylindrical formation, and consequently beingbalanced to rotate or partially rotate about its axis. In its operativeposition in which the magnetic axis passing through the north and southpoles of the magnet lies parallel with the Workpiece-supporting face thelines of magnetic flux emanating from magnet poles pass freely throughthe armature members and through .the soft iron or similar memberscomprising the workpiece-supporting face, and thence through the worpiece or workpieces placed thereon, the latter bei g thus held firmly inposition during the machining or other operation.

On however the magnet being moved angularly through an angle of throughthe medium of an operating knob, lever or similar device, the magneticaxis will be disposed at right-angles to a plane conte' ring theworkpiece-supporting face, and in this position the two armature memberswill form keepers and provide two flux leakage paths the lines ofmagnetic flux emanating from the egnet poles, which flux leakage pathsare of lou reluctance than that of the path including the soft iron orsimilar members of the workpiece-supporting face and the workpiece orworkpieces mounted thereon, the workpiece-supporting face being thusfree or substantially free from magnetic flux, the workpiece orworkpieces being consequently capable of removal from the Workholder.

In order that it may be clearly understood and readily carried intoeffect, the invention is hereinafter described with reference to theaccompanying drawing, wherein:

Figure 1 is a plan view of a magnetic workholder constructed inaccordance with the present invention;

Figure 2 is a longitudinal vertical section of the same on the line H-IIof Figure 1, the workholder being shown in its operative workholdingposition;

Figure 3 is an end elevation of the same;

Figure 4 is a transverse section on the line IVIV of Figure 2;

Figure 5 is a similar transverse section but showing the workholder inits inoperative position;

Figure 6 is a transverse section on the line VIVI of Figure 2;

Figure 7 is a perspective view of one of the magnets;

Figure 8 is a side elevation of the same;

Figure 9 is a side elevation of a magnet having pole-pieces of taperingform; and

Figures 10 and 11 are sectional views of the invention in a modifiedform.

The particular workholder illustrated incorporates three permanentmagnets of part-cylindrical formation, each of which magnets is somagnetised that its magnetic axis lies at right-angles to the axis ofrotation. It will be appreciated however that a plurality of magnets areemployed for convenience in manufacture where the production of acomparatively long magnet might present difliculties. Furthermore, byemploying magnets of more or less standard length, a workholder of anydesired length can be easily manufactured by selecting the appropriatenumber of magnets and assembling them together on a supporting shaft.

The workholder therefore comprises broadly a casing l composed ofnon-magnetic material and of box-like form, a workholding surface 2,permanent magnets 3 fixedly mounted on a shaft 4 which is partlyrotatable within suitable bearings, and armature members 5 locatedwithin the casing in such a position as to provide an alternative pathof lower reluctance for the lines of magnetic flux emanating from themagnets when the latter are moved through 90, which lines of magneticflux would otherwise pass through the workholding surface and workpieceand retain the latter in position. The alternative positions of themagnets and the paths taken by the lines of magnetic flux are shownclearly in Figures 4 and 5, a workpiece being diagrammatically shown inposition on the workholding face and indicated by the reference numeral5.

The fiat workholding surface comprises a series of soft iron or similarmagnetic members i separated by intervening non-magnetic spacing members8, the components being held together by means of non-magnetic bolts orrivets 9, the workholdin surface being finally machined to provide asmooth and flat work-supporting face. As will be clear from Figures 1, iand 5, the components 7 extend throughout the full length and width ofthe workholder and are of comparatively narrow cross-section, andconsequently a workpiece will be effectively maintained in position eventhough it is situated at the extreme end or lateral edge of theworkholding surface, a feature of considerable importance when it isdesired to machine a large number of small articles, such as washers orother small components, at one operation.

The casing l is closed at its ends by closure members 10 which carrybearings l I for the shaft i, the bearings being held in position bymeans of coverplates 12. The shaft and its associated magnets arecapable of being moved angularly through i. e. from the position shownin Figure 4 into the position indicated by Figure 5, the shaft beingformed with square extremities l3 either of which can receive anoperating handle M. A suggested means for limiting pivotal movement isshown in Figure 6, the shaft carrying a plate l5 formed with two notchesit either of which may be engaged by a spring-urged plunger H, the plateintermediate the notches, at l8, being of reduced radius, thearrangement being such that with the parts in the position-shown inFigure 6 rotational movement in a clockwise direction will be permittedthrough 90, whereas anticlockwise movement will be effectively preventeddue to the plate being of two different diameters.

The armature members are of laminated formation, as shown clearly inFigure 2, and are composed of a series of soft iron or similar metalstampings riveted or bolted together, as at IS, the armature membersbeing located within the easing by means of securing screws 20. Thearmature members are held in contact with the workholding surface 2 atits edges by means of securing screws 20a, and are shaped to correspondto the curvature of soft iron or similar pole-pieces 2! on the magnets,a minimum clearance being left between the pole-pieces and armaturemembers when the magnet system is in the operative workholding position,as in Figure 4. The polepieces are of such a length that when the magnetsystem is in the inoperative position shown in Figure 5, the armaturemembers will overlap the edges of the pole-pieces associated with thenorth and south poles of the magnets and provide an alternative path forthe lines of magnetic flux of shorter length and lower reluctance, thelines of magnetic force naturally taking the path of lower reluctancethrough the armature members without entering the workholding surfaceand workpiece. The path taken by the lines of magnetic flux in theoperative and inoperative positions of the magnet system is clearlyshown in Figures 4 and 5; and it will be observed that in Figure 5 thearmature members virtually shortcircuit the magnets, and incidentallyperform the function of keepers. It will be appreciated therefore thatwith the magnet system in the position shown in Figure 5 the workpiecewill no longer be attracted to the workholding surface, and consequentlycan be removed therefrom.

As it is virtually impossible to weld or braze the soft iron pole-piecesto the extremely hard magnet castings, it is necessary to employ someother method of attachment, and in the arrangement shown each pair ofpole-pieces are connected together by two plates 22 of brass or othernonferrous metal, which are brazed at their extremities to the edges ofthe pole-pieces, the noncircular fiat-sided formation of the magnetspreventing the pole-pieces turning about the magnets axes.

In order to secure the magnets firmly in position on their associatedshaft, non-ferrous members 23 of T shape are mounted in between themagnets, the T-shaped members projecting between the edges of thepole-pieces and being fixed to the shafts by securing screws 24, themagnets being thus keyed in position; the magnets and their associatedmembers 23 being sandwiched in position between annular shoulders 25 oneof which may be in threaded connection with the shaft to permit of themagnets being threaded thereon.

Due to the fact that the pole-pieces are always maintained out ofcontact with their adjacent armature members, the magnet system iscapable of being moved from its operative to its inoper ative position,and vice versa, with the minimumof effort, but if desired the effortrequired may be further decreased by constructing the polepieces of theoppositely-tapering formation shown in Figure 9.

The casing is shown provided with holdingdown feet 26 so that it can bescrewed in position on a workbench, but if desired the casing instead ofbeing of the channel section shown may be fitted with a secondoppositely-arranged holding surface as indicated at 21 in Figure 10 forengaging a metal workbench 28, or the metal bedplate of a millingmachine, or other machine too, so that the work-holder will be securedin position by the holding power of its own magnets. Alternatively, thearmature members may be continued downwards as shown at 29 in Figure 11into a position in which they project from or lie flush with the lowerpart of the casing I and are therefore capable of contacting any metalsurface 28 on which the workholder is placed.

The casing or its associated parts I2 may be provided with some suitableindicator for use in conjunction with the operating handle to indicatewhether the parts are in the workholding position or not, and toindicate the direction of permissible movement of the operating handle,and in such a case the extremities of the shaft may be so shaped as topermit of the handle being applied to the shaft in only one positionWhat I claim is:

1. A magnetic work holder comprising a non ferrous casing, a shaftrotatably mounted in said casing, a substantially cylindrical permanentmagnet fixed to said shaft, said magnet having diametrically oppositearcuate poles, two armature members spaced from said poles, saidarmature members being of concave configuration to conform to the shapeof said poles, a plurality of soft iron strips extending substantiallyparallel to said shaft, a plurality of non-ferrous strips alternatingwith said soft iron strips, all of said strips together providing awork-supporting surface, and supporting means maintaining said stripsadjacent respective faces of said two armature members whereby amagnetic circuit including said members, certain of said strips and awork piece supported on said surface may be held in place; and a pairformed, said strips being dimensioned so that a plurality of said softiron strips register with each of said faces and with the spaceseparating said faces.

2. A magnetic work holder according to claim 1 wherein said supportingmeans include a pair of soft bars parallel to said strips and enclosingsaid strips between them, and non-magnetic fastening means securing saidbars and said strips together, said bars being flush with said stripsand resting directly on the said faces of said armature members,respectively.

3. A magnetic work holder according to claim 1 wherein said permanentmagnet comprises a substantially cylindrical body, a pair of arcuatesoft iron pole-pieces disjoined from said body, and a pair ofnon-ferrous plates extending at opposite sides of said body, each ofsaid plates being joined to both of said pole-pieces whereby the latterare held in place.

4. A magnetic work holder according to claim 3 wherein said body hasflattened sides extending substantially parallel to the magnetic axis ofsaid body and located diametrically opposite each other, said platesbeing positioned adjacent said flattened sides, respectively.

5. In a magnetic work holder, in combination, a rotatable shaft; apermanent magnet fixed to said shaft, said magnet comprising asubstantially cylindrical body, a pair of arcuate soft iron polepiecesdisjoined from said body, and a pair of non-ferrous plates extending atopposite sides of said body, each of said plates being joined to both ofsaid pole-pieces whereby the latter are of spaced-apart armature memberspositioned at opposite sides of said magnet, said members being ofconcave configuration to conform to the shape of said pole-pieces.

6. The combination according to claim 5 wheret in said body hasflattened sides extending substantially parallel to the magnetic axis ofsaid body and located diametrically opposite each other, said platesbeing positioned adjacent said flattened sides, respectively.

7. The combination according to claim 5 wherein said pole-pieces are ofoppositely tapering configuration.

STANLEY ISAIAH HITCHCOCK.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,189,524 Randolph et a1 Feb. 6,1940 2,209,558 Bing July 30, 1940 2,280,437 Levesque Apr. 21, 19422,333,230 Beechlyn Nov. 2, 1943 2,347,023 Beechlyn Apr. 18, 1944

